Determining the effectiveness of legume-based cover crops on nitrogen benefits to a subsequent corn crop

Objectives:

• To assess the ability of annual legume-based cover crops planted following winter wheat harvest to provide a nitrogen (N) credit to a subsequent corn crop in comparison with frost-seeded red clover. This involves the evaluation of monoculture and mixed-species cover crops compared with a frost-seeded red clover cover crop under both twin row and conventional row planting and includes a cost of production analysis.
• To evaluate the effect of aboveground biomass removal of the cover crop on N benefits to the subsequent corn crop and assess the forage potential (including economic value) of these harvested cover crops.

• To quantify the effect of concentrating legumes in bio-strips on N credit to the subsequent corn crop.

Impacts:

• We provided information about how altering winter wheat row-spacing affects the uniformity of a red clover stand and N credit to the subsequent corn crop.
• New information on the potential of annual clovers (Berseem and Balansa), that are available on the Ontario market, to provide an N credit was provided.
• Producers have been provided with knowledge on the value of different legume cover crops and legume-based cover crop mixtures as fall forage, allowing them to use cover crops as a dual-purpose crop.
• The impact of removing the aboveground biomass of the cover crop on any benefits to the following year’s corn crop was determined. This informed whether it was worth it economically to harvest the cover crop as forage.
• The testing of the effect of planting legume and radish cover crops in bio-strips on the following year’s corn crop (yield and N credit) allows producers to make an informed choice about how to best plant their cover crop (uniformly across the field or in bio-strips).

Scientific Summary:

In southwestern Ontario, there is an opportunity to reduce the use of N fertilizer applied to corn through the use of preceding legume-based cover crops. Red clover that is frost-seeded in the spring into a standing winter wheat crop has demonstrated significant benefits to a subsequent corn crop in terms of providing an N credit. However, red clover stands frequently suffer from inconsistent year to year growth and non-uniformity across a field, which has reduced the uptake of using red clover by farmers. Annual cover crops planted after winter wheat harvest, specifically those that include legumes, have the potential to be an alternative to red clover and provide a N credit to the following crop. Finally, if cover crops can be grown with the potential for harvest as forage, more farmers may be likely to adopt cover crop use. However, how the removal of aboveground cover crop biomass impacts any benefits to the subsequent crop remains to be determined.

In the proposed research, we set out to provide information about how altering winter wheat row spacing affects the uniformity of a red clover stand. In addition, annual legume-based cover crops (in monocultures and in oat and radish mixtures) including Berseem clover, Balansa clover, and Austrian winter pea were compared with red clover in terms of being able to deliver a N credit to a subsequent corn crop. By collecting yield and forage quality data of cover crops over three years, the potential of using a cover crop for fall forage was assessed. Finally, we aimed to compare whether the placement of the legume and radish as a bio-strip can improve any benefits to the next year’s corn crop.

Results:

The proposed project leveraged an experiment that started in the fall of 2020 with the planting of winter wheat, to which cover crops treatments were planted in August 2021, and corn planted in 2022. The whole experiment was repeated two additional times with a final corn harvest in 2024. The field experiment was set-up in a strip-plot design with 15 cover crop treatments and a no cover crop control plot. After winter wheat harvest, annual legumes, planted alone and in mixtures with oats and radish, were compared to a frost-seeded red clover cover crop. The annual legumes included Berseem clover, Balansa clover, and Austrian Winter Pea (peas). Three years of cover crop data were collected and analyzed. In general, red clover biomass was variable across the three years, with oats and oat-based mixtures being more consistent. In terms of annual legumes, Balansa clover failed to establish well in all three years of the trial. Berseem clover produced a low but harvestable biomass in two of the three years. Peas were somewhat more reliable but still were not a high biomass producer when planted in monoculture. Generally, all cover crops produced good forage quality; however, if concerned about producing a higher quality forage, a mixture such as oats and pea or oats-pea-radish may be a better choice than monoculture oats.

In 2022, the cover crop treatment had a significant effect on corn yield and fertilizer N credit, with red clover resulting in the highest corn yield (11.35 Mg ha^-1) and the no cover crop control producing the lowest corn yield (7.16 Mg ha^-1). Fertilizer N credits ranged from ‑23 to 93 kg N ha^-1. Minimal differences in corn yields were found across cover crop treatments in 2023; however, the twin row red clover treatment was statistically greater than the control (despite having a low cover crop biomass). No significant differences in corn yield or fertilizer N replacement value among cover crop species were found in 2024.

Overall, this research supports that red clover can be a valuable cover crop in terms of providing yield and N benefits to a subsequent corn crop, but this is dependent on good establishment. In terms of the other legumes tested, peas performed better than the two annual clovers but generally did not produce high yields as a monoculture. Harvesting a cover crop for forage did reduce corn yield the next year but the reduction was numerically small (~0.4 to 0.60 Mg ha^-1) and may be justified due to the economic benefit of harvesting a cover crop for forage.

External Funding Partners:

The project was funded in part by the Ontario Agri-Food Innovation Alliance, a collaboration between the Government of Ontario and the University of Guelph. Funding was also provided by the Ontario Ministry of Agriculture, Food, and Rural Affairs (OMAFRA) Highly Qualified Personnel Scholarship (HQP) program. The HQP Program is funded by the Ontario Agri-Food Alliance and the University of Guelph’s Food from Thought research program and supports the development of skilled graduates who can meet the changing demands of the agri-food and rural sector.

Project Related Publications:

None.